This invention relates to an actuating device suitable for use as a model railroad switch machine, although it could be used in any application requiring a relatively slow throw.
Referring to the model railroad switch machine art, the standard of the industry for many years has been the so-called twin coil machine. This is a solenoid actuated device which produces a loud, instantaneous throw of the switch points. This type of device has several disadvantages. It is easy to burn out the solenoid. The movement is hard on the switch points as they are forced to absorb the impact of being slammed against their associated rails. And the instantaneous movement does not provide a prototypical action, since full-size switch points require a certain amount of time to be thrown. The fast action of a solenoid switch machine does not reproduce the slow motion action of full-sized switches. In the eyes of a serious modeler, this is a significant defect in the twin coil machines.
The problem of the fast versus slow motion action has been addressed by so-called jackscrew machines. These machines use a small electric motor driving a long screw engaging a sliding member. While these machines provide a prototypical action, they are noisy and unreliable. A flexible coupling between the screw and the motor is a common source of failure.
Another approach to a slow motion switch machine uses a reduction gear train driven by a motor having a stall current that is so low that the motor can be continuously stalled without damaging it. Previous devices of this type have applied the full torque of the motor to the switch points. That is, the motor throws the switch points up against a rail which must provide the resistance required to stall the motor. This risks damage to finely-constructed switch points. Another drawback of previous switch machines utilizing a stalled motor concept has been the difficulty of providing auxiliary contacts which are advantageously used for providing signals indicative of the switch condition.